Degradation and defluorination of C6F13 PFASs with different functional groups by VUV/UV-based reduction and oxidation processes

Structural diversity can affect the degradability of per- and polyfluoroalkyl substances (PFASs) during water treatment. Here, three PFASs with different functional groups—C₆F₁₃-R, PFHpA, PFHxS, and 6:2 FTS—were degraded using vacuum ultraviolet (VUV/UV)-based treatments. While fully fluorinated PFASs—PFHpA and PFHxS—were degraded faster in the VUV/UV/sulfite reaction than in VUV/UV photolysis, VUV/UV photolysis was more effective for degrading 6:2 FTS by OH radicals produced through photolysis of water. PFCAs such as PFHxA, PFPeA, and PFBA were formed by VUV/UV photolysis of PFHpA and 6:2 FTS, but the PFCA formation was inhibited in the VUV/UV/sulfite reaction. The degradation of the three PFASs in the VUV/UV/sulfite reaction was mainly carried out by H/F and SO₃^•-/F exchange mechanisms, mediated by hydrated electrons (e_aq^-) produced in the reaction. During the VUV/UV/sulfite reaction, PFCA precursors were first formed as transformation products, which were further transformed into PFCAs by the following VUV/UV/H₂O₂ reaction, implying enhanced defluorination of three PFASs. Our results indicate that VUV/UV-based treatments can be an option for PFAS degradation and defluorination by combining advanced reduction and oxidation processes and utilizing both e_aq^- and oxidative radicals.